Cycling through a sequence of scenes to represent day and night following one another during a game.

Suppose we want to have a sequence of nights and days in our game, with one scene to govern each daylight condition.

"Night and Day"
The sun is a backdrop. It is everywhere. The description is "Currently out of sight."
Night is a recurring scene. Night begins when play begins. Night begins when Dusk ends. Night ends when the time since Night began is 3 minutes.

Notice that our two conditions for the beginning of Night are not in conflict: it will be night-time when the game begins, and then night will also recur every time the Dusk scene ends.

When Night begins:
   say "The sun falls below the horizon and the temperature drops abruptly to well below zero.";
   now the description of the sun is "Currently out of sight."
Dawn is a recurring scene. Dawn begins when Night ends. Dawn ends when the time since Dawn began is 1 minute.
When Dawn begins:
   say "The sun appears on the horizon.";
   now the description of the sun is "It is tiny and weak.".
Day is a recurring scene. Day begins when Dawn ends. Day ends when the time since Day began is 3 minutes.
When Day begins:
   say "The sun is now properly up."
Dusk is a recurring scene. Dusk begins when Day ends. Dusk ends when the time since Dusk began is 1 minute.
When Dusk begins:
   say "The sun has passed across the sky and is on the verge of setting."
Cratered Landscape is a room. "The ground here is [if Night is happening]dim silver, with the craters visible as darker splotches[otherwise]the color of dried blood; here and there it is also rippled by impact craters[end if]. The horizon curves visibly."
Test me with "z / z / z / look / x sun / z / z / z / z / z / z / z".
Test me with "z / z / z / look / x sun / z / z / z / z / z / z / z".
Cratered Landscape
The ground here is dim silver, with the craters visible as darker splotches. The horizon curves visibly.

>(Testing.)

>[1] z
Time passes.

>[2] z
Time passes.

>[3] z
Time passes.

The sun appears on the horizon.

>[4] look
Cratered Landscape
The ground here is the color of dried blood; here and there it is also rippled by impact craters. The horizon curves visibly.

The sun is now properly up.

>[5] x sun
It is tiny and weak.

>[6] z
Time passes.

>[7] z
Time passes.

The sun has passed across the sky and is on the verge of setting.

>[8] z
Time passes.

The sun falls below the horizon and the temperature drops abruptly to well below zero.

>[9] z
Time passes.

>[10] z
Time passes.

>[11] z
Time passes.

The sun appears on the horizon.

>[12] z
Time passes.

The sun is now properly up.

If we run this example and then have a look at the scenes index, we'll see that the cycle is listed through thus:

Night (recurring)
   Dawn (recurring)
      Day (recurring)
         Dusk (recurring)
            Night

with the second "Night" in italics, to indicate that it is a repetition of the same scene that has already been listed above.